July, 1935
OsSERVATXONS ON THF:
ter employing this substance has been proposed and the effects of diflerent conditions upon the khavior have been examined. A null method of csmparison has been proposed and found satisfactory to 3% in absolute value. Other variatisns of the stltndard actinometer (as the tempera-
[CONTRIBUTION FROM THE
RAKEEARTHS.XLIV
I. 159
ture coefiicimts) were investigated with the aid of this null method. Other actinometers which used molrochloroseetic add and crystal violet leucocyanide were tested and found to be less desirable. CAMBRIDGE,
MAS.
RECEIVED MARCH6, 1935
DEPARTMENT OF CHEMISTRY OF THE UNIVERSITY OF ILLINOIS]
Observations on the Rare Earths. XLIV. Preparation of Anhydrous Rare Earth Compounds by the Action of Fused and Solid “Onium” Salts on the Oxides BY JAMES B. REEDWITH B. S. HOPKINS AND L. F. AUDRIETH Recent studies on the solubilities of rare earth compounds in non-aqueous solvents’ and on the preparation of rare earth amalgams by electrolysis of non-aqueous solutions of their salts2 have brought about the necessity of preparing anhydrous rare earth compounds, reasonably free from basic materials, and in considerable quantities. The compounds most extensively used in these studies are the halides which are exceptionaIly difficult to prepare in the anhydrous form. None of the many methods previously suggested for their preparation have proved entirely satisfactory when applied to relatively large quantities. It has been found that oxides of typical rare earth elements such as lanthanum, neodymium, samarium and yttrium dissolve in such fused salts as pyridine hydrochloride,2dammonium nitrate:’ hydrazine hy drochloride, hydroxylamine hydrochloride, ammonium thiocyanate3and ammohium a ~ e t a t e . They ~ react with solid ammonium chloride, ammonium bromide and ammonium iodide. These reactions are all of the same general character and may be represented by the typical equation LatOs
+ I~JNHXI= 2LaCla + 0“s
+ 3HlO
This reaction is readily understood if it is recognized that “onium” salts in the fused and solid states are acids according to the Bronsted defini(1) Hopkins and Quill, Proc. Nul. Acad. Sci., 19, 64 (1933). (2) (a) Audrleth, Jukkola, Meints and Hopkins, THISJOURNAL, 1S, 1805 (1931); (b) Meints, Hopkins and Audrieth, 2. anorg. allg6m. Chem , a l l , 237 (1933); (c) Jukkola, Audrieth and Hopkins. Tats JOURNAL,16, 303 (1934); (d) Hopkins and Audrieth, Trans. A m . Electrochem. Sot., 66, 135 (1934). (3) The resulting product composed of an intimate d x t u r e of rare earth thiocyanate and excess ammonium thiocyanate is soluble in alcohol, acetone, pyridine and liquid ammonia. (4) Lanthanum and neodymium oxides dissolve quite readily in fused ammonium acetate, whereas only incomplete reactions occur when the less basic rare earth oxides are employed If these melts are heated in a vacuum at temperatures between 130-150° residues consisting essentially of the anhydrous acetates may be obtained.
tion.6 In spite of the fact that water is one of the reaction products, the presence of excess ammonium chloride, by virtue of its acidic nature, prevents the hydrolysis of the lanthanum chloride. Hence, when carried out under proper conditions the above reaction and others of the same type may be used for the preparation of anhydrous rare earth compounds.
Experimental Preparation of Anhydrous Rare Earth Chlorides?-When ammonium chloride and oxides of the rare earth elements are mixed by grinding together in a mortar the odor of ammonia becomes distinctly noticeable, indicating that some reaction takes place even at room temperature. Up to a temperature of about 190” the reaction appears to be a very slow one, but above this temperature it proceeds vigorously. If twice the theoretical amount of ammonium chloride is used (for instance, 150 g. of NHICl to 75 g. of Nd203) the reaction mixture soon becomes completely soluble in water.’ A considerable portion of the (6) Audrieth and Schmidt, Proc. N a f . Acad. Sci., 20,221 (1934). (6) Various methods are listed in the literature for the dehydration of hydrated chlorides by heating in the presence of an excess of ammonium chloride. These procedures usually involve the addition of a large excess of ammonium chloride t o a saturated solution of the chloride, after which the solution is evaporated t o dryness and the mixture heated carefully by itself or in an atmosphere of hydrogen chloride. The method described by the authors not only eliminates this cumbersome procedure, but effects a considerable saving of time. The essential principle of preventing basic salt formation by the presence of the “onium“ salt seems not t o have been clearly defined heretofore and its elucidation (see Ref. 5 ) has enabled the authors to apply this method t o the preparation of many other anhydrous chlorides. It should be pointed out t h a t Hodgkinson [ J . Soc. Chcm. I n d , 33, 445 (1914)] describes a method for the preparation of anhydrous chlorides, by mixing the oxides with a small excess of ammonium chloride and gradually dropping the mixture into a red hot crucible Repeated trials of this method have shown t h a t complete reaction is never obtained and that considerable loss of material is involved. (7) In the case of cerium dioxide complete conversion t o the chloride was not obtained.
1160
JAMES
B. REEDWITH B. s. HOPKINSAND L. F. AUDRIETH
VOl. 57
excess ammonium chloride may then be driven water and found to have the approximate comoff by continued heating in air. However, any position required for the compound, LaOI. The reaction of ammonium iodide upon rare attempt to drive off all of it in this manner invariably results in the formation of some basic earth sulfides8was also investigated in a prelimimaterial. The excess ammonium chloride is nary fashion. The rare earth sulfides were found therefore best removed by heating the mixtures at to react with excess ammonium iodide in an evacu300-320” in a vacuum in an all-glass apparatus ated, sealed Pyrex tube a t 450-500’. The odor of hydrogen sulfide was distinctly noticeable when designed specifically for this purpose. The anhydrous chlorides prepared by this the tubes were opened. The reaction mixture method are obtained in finely powdered form. was then heated in vacuum until all volatile subThey are extremely hygroscopic and hiss on addi- stances were removed completely. The product, tion of water. Their water solutions are usually which was bluish-gray in color, was only partially clear. No ammonia can be detected upon heat- soluble in water. Analysis for the iodine-rare ing with excess sodium hydroxide. The chlorides earth ratio in the water soluble portion indicated are also readily soluble in alcohol and have been that at least partial reaction with formation of used successfully for the preparation of rare earth the normal iodide had taken place. Further work is being done on this problem.9 amalgams2 Yields of 85 to 95% were obtained. The resummary maining rare earth material was not lost, but was 1. Reactions between rare earth oxides and recovered almost quantitatively from material adhering to the vessels and that used in solubility a number of fused “onium” salts are described. 2. Rare earth oxides react a t higher temperatests during the course of the reaction. Analyses of typical batches of rare earth chlorides prepared tures with ammonium chloride and ammonium bromide to yield the corresponding halides. The in this manner are given in Table I. excess of “onium” salt may be removed by heating TABLEI in a vacuum to give the anhydrous rare earth Rare earth, % Nature of oxide Calc?’ %ound Calcd. Found chlorides and bromides. 56.65 56.61 95% La, 5% Pr 43.35 43.46 3. Rare earth sulfides, prepared by reduction 56.78 56.28 60% La, 40% Pr 43.22 43.29 of the sulfates with sugar charcoal, react partially 57.57 57.3 Pure NdzOs 42.43 42.77 Atwith solid ammonium iodide at 450-500’. Preparation of Anhydrous Rare Earth Bro- tempts to prepare the anhydrous iodides by the mides.-Ammonium bromide was found to react action of ammonium iodide upon rare earth oxides readily with rare earth oxides. By carefully resulted in the formation of the basic iodide. heating the reaction mixture in air a completely URBANA,ILLINOIS RECEIVED MARCH18, 1935 soluble product could be obtained. This mix(8) Rare earth sulfides are generally prepared by heating the sulture was then heated in a vacuum a t about 300’ fates or oxides in a stream of hydrogen sulfide a t red heat. This is not readily adaptable t o the preparation of large quantities. to remove the excess ammonium bromide. The method I t was found that the anhydrous rare earth sulfates could be reduced anhydrous bromides prepared in this way were readily t o the sulfides by heating with an excess of sugar charcoal a t bright red heat for about an hour. The resulting product contained usually completely water soluble. The following small amounts of carbon and possibly some rare earth oxides. Sulis an analysis of lanthanum bromide prepared fides prepared in this manner were used in the current investigation. Their preparation and a study of their properties will be made the in this manner. subject of a future communication. Required for LaBrt Found
La, %
Br, %
36.70 36.52 36.27
63.30 62.62 62.16
Reaction of Ammonium Iodide with Rare Earth Oxides and Sulfides.-Solid ammonium iodide and lanthanum oxide react readily at 200’. However, even if the reaction was carried out in a vacuum the final product was always insoluble in
(9) Various other reactions were investigated in an attempt to prepare anhydrous rare earth iodides. Anhydrous lanthanum chloride was heated in a vacuum with excess ammonium iodide. The resulting product contained both iodine and chlorine. Repeated addition of ammonium iodide and heating failed t o displace all the chlorine from the product. The reaction between anhydrous lanthanum acetate and ammonium iodide went only partially t o completion. Thermal decomposition of anhydrous lanthanum iodate yielded the pure basic iodide, LaOI. Ammonium iodide and lanthanum chloride react in absolute ethanol t o precipitate some of the ammonium chloride. Here again the reaction could not be made t o go to completion.
